linux-kernel - Re: dsa: mv88e6xxx: serdes link without phy

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Date:   Thu, 1 Oct 2020 03:24:10 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>
Cc:     "vivien.didelot@...il.com" <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: dsa: mv88e6xxx: serdes link without phy

>                          port@8 {
>                                  reg = <8>;
>                                  label = "internal8";
>                                  phy-mode = "rgmii-id";
>                                  fixed-link {
>                                          speed = <1000>;
>                                          full-duplex;
>                                  };
>                          };
>                          port@9 {
>                                  reg = <9>;
>                                  label = "internal9";
>                                  phy-mode = "rgmii-id";
>                                  fixed-link {
>                                          speed = <1000>;
>                                          full-duplex;
>                                  };
>                          };

> 
> The problem is that by declaring ports 8 & 9 as fixed link the driver 
> sets the ForcedLink in the PCS control register. Which mostly works. 
> Except if I add a chassis controller while the system is running (or one 
> is rebooted) then the newly added controller doesn't see a link on the 
> serdes.

Hi Chris

You say SERDES here, but in DT you have rgmii-id?

Can you run 1000Base-X over these links? If you can, it is probably
worth chatting to Russell King about using inband-signalling, and what
is needed to make it work without having back to back SFPs. If i
remember correctly, Russell has said not much is actually needed.

   Andrew